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000
FXUS65 KPSR 112100
AFDPSR

Area Forecast Discussion
National Weather Service Phoenix AZ
200 PM MST Thu Apr 11 2024

.SYNOPSIS...
Persistent high pressure over the region will result in temperatures
warming to their warmest readings so far this year, with
afternoon highs in the nineties across the lower deserts through
Friday. Weak low pressure approaching our forecast area will
result in widespread breezy conditions Friday afternoon. A more
potent low will then affect the Desert Southwest this weekend,
helping to generate continued breeziness and leading temperatures
on a cooling trend toward below-normal levels.

&&

.DISCUSSION...
Dry and tranquil conditions are being observed across much of the
western CONUS as upper-ridging continues to encompass the region.
Temperatures across the Desert Southwest have quickly increased
since this last weekend, with many areas yesterday, especially
out in SE California and SW Arizona, experiencing their first 90
degree temperatures since last Fall, and this warming trend is not
expected to stop today. Lower and middle 90s will be common
across the lower deserts this afternoon, with a few readings of
95+ likely (60-80%), mainly for areas in and around the lower
Colorado River and Imperial Valleys. The Sky Harbor ASOS has
already reached the 90F mark today, making it the first time since
November 7th of last year that the station has recorded
temperatures in the 90s. Afternoon highs Friday will be similar
to today, albeit a degree or two cooler as 850mb temperatures will
decrease slightly. These unseasonably-warm temperatures will
result in widespread Minor HeatRisk, meaning individuals who are
extremely sensitive to heat and those who plan to be outdoors for
extended periods should take extra precautions.

Weak low pressure, currently located several hundred miles off the
coast of the Baja Peninsula, will advance eastwards towards the
Desert Southwest over the next 24-36 hours, reaching just west of
our forecast area by Friday. The main forecasted impact associated
with this system continues to be breezy to locally windy conditions
Friday afternoon and evening as this system helps to increase the
regional pressure gradient. It still appears that the NBM
deterministic forecast is being slightly too aggressive with
gusts, indicating a fairly large swath of advisory level wind
gusts (>40 mph) over southwestern Arizona. However, flow at 850mb
is only expected to be between 20-30 kts, meaning that widespread
surface gusts between 25-35 mph, with isolated higher gusts, would
be a more realistic outcome. Regardless, the most enhanced winds
will be focused over much of SW Arizona and the usual breezy spots
out in SE California, with perhaps occasional terrain influenced
gusts reaching above advisory levels over western Imperial County
Friday evening. Models point towards mid-level flow becoming
stronger over far southwestern Arizona, elevating to 30-40 kts by
Friday evening. However, it is unlikely that gusts that strong
will be observed at the surface as this enhanced flow is expected
to develop outside of the peak mixing timeframe, making it harder
to bring those higher momentum winds down to the ground.

The aforementioned system will eventually merge with a more
potent low that will be diving south along the West Coast as we
head into the end of the week and into the weekend, with the
center of circulation projected to be just off the California
Coast by Saturday. The proximity of this disturbance to the Desert
Southwest will help reinforce the regional pressure gradient,
reestablishing breezy to windy conditions across the region
Saturday afternoon. Gusts look to be similar to what will be seen
on Friday, with decent chances (60-80%) of seeing advisory level
gusts once again over parts of SE California. Enhanced breeziness
may last into Monday for some areas as the base of the low moves
inland and slides eastward across the lower deserts by the end of
the weekend and into the start of next week. The other noticeable
impact with this system will be a downward trend in temperatures
towards below normal levels, with many lower elevation locations
not even getting out of the 70s on Sunday and Monday. As mentioned
in the previous discussion, rainfall potential with this system
remains near zero, with the limiting factor being the lack of
anticipated moisture flux over the region. However, with cooler
air in place aloft, combined with enough forcing from the low and
an associated PV anomaly, a few sprinkles and light showers,
mainly over the Arizona high-terrain, may conceivably be squeezed
out on Monday.

&&

.AVIATION...Updated at 1137Z.

South-Central Arizona including KPHX, KIWA, KSDL, and KDVT:
Light winds will prevail through Friday morning at all terminals
with wind speeds aob 8 kts. Wind directions will still tend to
follow typical diurnal trends, however confidence in the westerly
shift is low and may not occur until as late as 01-02Z, as well as
be short-lived. Between 21-02Z, SW-SE variability is anticipated.
Easterly winds should reestablish by 05-07Z tonight. SKC skies
will prevail.

Southeast California/Southwest Arizona including KIPL and KBLH:
Light winds will prevail through the TAF period at both terminals,
with speeds mainly aob 7 kts. At KIPL, wind directions will favor
W through mid-morning with some variability before shifting E.
Winds then return W this evening. At KBLH, NW winds this morning
are expected to gradually veer to the SSW by this evening with
periods of light variability. SKC skies will prevail.

&&

.FIRE WEATHER...
Dry conditions and above normal temperatures will prevail through
at least Friday as high pressure builds over the region. Today,
winds will be fairly light, 5-15 mph, across all districts, with
directions following typical diurnal trends and terrain
influences. The environment will be quite dry through the
remainder of the week, as temperatures also warm into the 90s.
Minimum afternoon RHs will fall below 15% each day through
Saturday with limited overnight recover (up to 30-45% RHs). A
weak disturbance Friday will lead to widespread breezy conditions,
especially during the afternoon and evening. Winds will be
strongest in Southwest AZ with southerly gusts pushing as high as
35-40 mph, while most other areas see peak southerly gusts up to
25-35 mph. Another system this weekend, passing mainly to the
north, will lead to continued daytime breezy to locally windy
conditions, bring cooler temperatures, and increase RH values
slightly. These breezy conditions, especially Friday and Saturday,
could lead to elevated fire weather conditions where there are
any dry fine fuels.

&&

.PSR WATCHES/WARNINGS/ADVISORIES...
AZ...None.
CA...None.
&&

$$

DISCUSSION...RW
AVIATION...Benedict
FIRE WEATHER...Benedict